The present invention relates in general to magnetic drive pumps, and in particular, to an encapsulated magnet for a magnetic drive pump and method of making the same.
A typical use for the present invention is in a pump having a magnetic drive. A magnetic drive pump has an outer annular magnet turned or rotated by a motor. An annular inner magnet is disposed within the outer magnet and is carried on a pump shaft. The inner magnet is isolated from the outer magnet by a thin metallic or plastic cup.
The inner magnet of such pumps includes a magnet and flux ring assembly which operates in the process fluid that is moved through a system by the pump. If the process fluid such as water contacts the assembly, the magnet and flux ring may corrode or rust. Additionally, the assignee of the present invention has researched using rare earth materials for the magnet for use in magnetic drive pumps. These rare earth materials are highly susceptible to corrosion when immersed in fluids such as water.
Several methods have been tried in order to correct the problem. One presently used method includes placing the magnet and flux ring inside a stainless-steel shell and molding an outer cover over the exposed assembly. Such a construction, disclosed in commonly assigned U.S. Pat. No. 4,414,523, is not adequate for all applications. Additionally, various coatings and platings have been applied to the magnet outer surface. Such methods and materials are not known to withstand contact with all process fluids and to maintain a leak-free encapsulation of the magnet.
One manufacturer, March Pump, has developed an over-molded vane pump using a two-step molding process for the magnet and impeller. The seam between the first molding step material and the second molding step material does not ensure a leak-free joint.